LLC resonant power conversion technology can be widely used in non-contact electric vehicle charging stations, electromagnetic induction heating, switching power supply and non-contact energy transmission. As an existing solution method, phase-locked loop control technology has been used in LLC resonant converter now to solve its reliability problems. LLC resonant converter has some virtues such as high efficiency, low electromagnetic interference, and simple control in circuitry; and as shown by FIG. 1, a resonant current signal is sampled by a current transformer and is sent to a phase-locked loop circuit, and is compared with a phase-locked loop output signal at phase to generate a phase error voltage; after filtering, the LLC resonant converter controls an oscillator synchronized with the current signal, and accomplishes synchronization between a main resonant loop current and the control signal, and so the S1 and S2 electrical switches can be controlled on and off separately by a split-phase controller. However, the key problems of this technology are that an error voltage generated by the phase locked loop should go through a filtering network so it takes 5-10 cycles to prevent the LLC resonant converter to fall into a hard-switching state; and the converter cannot realize a real-time response to changes and dynamics of the LLC resonant converter bus voltage or random load changes, so the reliability issues have not been completely resolved.
In 2004, the U.S. International Rectifier company produced an IR2159 serial LLC resonant converter controlling chips in energy-saving lamps field, but they couldn't fundamentally solve the key reliability problem of the LLC resonant converter yet. The reason is that the phase-locked loop control mode was still adopted in the IR2159 serial chips; the lowest frequency limit of an oscillator has been adjusted and controlled by an integrating circuit, so as a result, not every turning-on pulse signal to the LLC resonant converter can be controlled instantly, and the reliability is low; it is still hard to make a large scale production by using this series of chips.
Here is the technical proposal of the published patent in P.R.C (the application number is 200680010615.6): a converter can shut down the turning-on pulse to ensure a zero-current and zero-voltage switching-on in the next half cycle if a LLC resonant main loop current is above a predefined current maxim, or a main loop current holding time is longer than a time predefined by a control system, or the main loop current has passed zero (a resonant capacitor will pick up a voltage signal). But there is a problem in this kind of controlling method: zero-current and zero-voltage switching on and off conditions of S1 and S2 would be lost if the current has passed zero, because the remained resonant energy of a LLC main resonant tank is not enough to keep the same phase current flowing to the next half turning-on signal cycle in which the corresponding power electronics device is in a reverse conduction, so there is no natural zero-current-switching (ZVS) or zero-voltage switching (ZCS) states. In addition, the control theory is imperfect because a main loop dispersion parameter and load uncertainties would result in incomplete control based on a timing device and in shutting down the turning-on signal pulse by detecting the main current zero-crossing.
Invention Content
The present invention is to provide a full voltage range LLC resonant converter and its controlling method, and to achieve a LLC resonant converter running in a full input voltage range; under the condition that a line in AC voltage only passes through a rectifier without energy storing in a capacitor and freewheeling in an inductor at an output port of a rectifier, a rectified voltage with a full-wave rectified sine waveform will be a power supply for a bus of the LLC resonant converter directly; at any time when a bus voltage of the LLC resonant converter changes from 5% of its maximal voltage (Vmax) to Vmax, a main loop energy quantifier can instantly detect remaining resonant energy of the LLC main loop, and electric device S1 or S2 of the LLC resonant converter will be turned off if the LLC main tank energy decreases to the required energy scale that can ensure corresponding electric switch to work in ZVS on state, and so the remaining resonant energy can make the corresponding electronic switch turned on in ZCS. Without energy storing in a capacitor and freewheeling in an inductor, the probability of a failure in an electrolytic capacitor is inexistence, and the reliability of the LLC resonant converter can get a fundamental guarantee. So in the AC input working situation it becomes true to design a LLC resonant converter to be a solid state converter, and the lifetime of the LLC resonant converter would be equivalent to the lifetime of semi permanent devices used in the LLC resonant converter, then the aforementioned problems in background technology can be resolved fundamentally.